This disclosure describes embodiments of systems, controllers, and methods to provide improved control and coordination of a multiplicity of electric distribution grid-connected distribution units, such as energy storage units deployed over a geographically-dispersed area. The units may be very similar to those described in U.S. Pat. No. 6,900,556 and commonly referred-to under names such as Distributed Energy Storage (DES) and Community Energy Storage (CES). An alternative design of units that may be adapted, used, deployed or controlled in accordance with the embodiments herein described is described in U.S. Pat. No. 7,050,311 and referred-to as an “Intelligent transformer.” In summary, these units are self-contained energy storage systems consisting typically of a storage battery capable of holding 25 kWH of energy or more, an inverter, and a local control system with a communication interface to an external central control system responsible for coordinating their function within the distribution grid. These external central control systems are commonly referred to under names such as the HUB controller or the Distributed Energy Management (DEM) controller. The system consisting of the controller and the storage units is commonly referred-to as a Virtual Power Plant. Under sponsorship of the Electric Power Research Institute (EPRI), the functional requirements for a very simple control system for coordinating the operation of these storage units have been cooperatively developed and placed in the public domain.
The primary function of the DES unit is to assist the utility in reducing peak demand (referred to commonly as “peak shaving” or “load following”) to defer or eliminate a regional need for additional generating capacity. Other valuable features of the DES unit include the ability to provide reactive power compensation, to provide voltage support, to provide backup power for stranded customers when the main source of supply is temporarily unavailable, and to provide frequency support (ancillary services). An extensive description of the requirements of the basic DES unit, from the customer (electric distribution utility) point of view is contained in the EPRI DES Hub and Unit Functional Requirements Specifications. Other functions allow the DES unit to facilitate the connection of various renewable energy sources into the grid. This includes providing energy storage or buffering during periods of weak demand, and conversion from DC to AC and AC to DC.
In order to coordinate the functions of the remote DES units, the external central controller DEM requires communications between the DEM and each storage unit to obtain operational performance data and to send commands from the DEM to the storage units. The DEM may also be in communication with devices such as Transformer Breakers, Feeder Breakers, and/or Tap Controller power monitors. The DEM performs communications at regular intervals to evaluate information obtained and to send updates to the fleet. The DES is designed to target deployments that are highly distributed across a large number of locations, employing a variety of telecommunications solutions for communications. Such scattered distribution means that communications can be unreliable, low bandwidth, and potentially carrying high operating costs.
Accordingly, it is desirable to provide methods and systems for reducing the frequency of communications in highly distributed energy distribution systems. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.